It’s time for another installment of “The Power of Post!” Lately, I’ve been shooting a good amount of architectural and urban photography. It’s one subject that’s really made me appreciate the power and usefulness of tilt-shift lenses.

On the left is an image with uncorrected converging verticals; on the right, a similar shot with the perspective corrected in post. The corrections are certainly not perfect, but it’s a much more realistic representation of what the human eye sees when viewing the scene.

The technical term for the converging vertical perspective phenomenon is “keystoning.” PhotographyBlog.com provides a great explanation:

The word originates in architecture and bridge building, where the trapezoid shaped middle stone in the top of an arch that holds all the other stones in position is called a keystone. In photography, keystoning occurs whenever you tilt your camera up or down. When photographing a tall building, you’ll often tilt the camera upward both in order for the building to fit into the frame and in order for you to get rid of any unwanted foreground. This is when the vertical lines of the building converge towards the top in the photo…

This will happen irrespective of the type of lens used, although the effect will indeed be more pronounced with wide-angle optics, simply by virtue of their being more powerful at creating a sense of perspective – keystoning is, after all, a vertical perspective effect. But if you refrain from tilting your camera and manage to keep it perfectly level, you won’t have to deal with keystoning, even if you use an ultra-wide lens.

Although tilt-shift lenses have seen recent popular resurgence in the production of “miniature world/ toy world” (Miniature Faking) photography, their intended use is the correction of the keystoning problem in the field, as the photo is being made. They are lenses specifically designed to fill the architectural niche; because of this- and the fact that they’re incredibly difficult to manufacture- they are inordinately expensive. (Check out Nikon’s Wide Angle PC-E Nikkor 24mm f/3.5D ED on B&H , for example. Yikes!)

The fun part comes when you use a lens that’s yet unsupported by Adobe, such as my Tokina 12-24mm f/4, an awesome ultra-wide lens. (I still want to marry Lightroom) You must use the individual attribute sliders in the ‘Manual‘ panel of the Lens Corrections dialogue:

Fortunately, Adobe has made these controls very intuitive to use, and it takes no time at all to get a feel for how to manually correct keystoning in your photos.Here are a couple of examples:

Photo taken at the top of the Chicago Art Institute’s Modern Wing, looking toward the skyline; you can see that the buildings on the right side of the frame are distorted, and leaning slightly in toward the center.

I made the following adjustments in the Manual Lens Corrections module:

Distortion: +13Vertical: -8

Horizontal: -6

Rotate: +.8

I usually begin with the vertical, then horizontal, adjustments and move to the other sliders as needed. The result (in addition to curves & brightness adjustments) is a photo with no converging verticals:

Huzzah!

Another Example- you can see that, on the right, the two buildings lean toward each other in the center of the frame as a result of the extreme low perspective. I was tilting the camera up quite a bit to compose the shot.

On the right, the same photo shows improvement, but is not completely free of keystoning. To completely eliminate converging verticals in the image would require an undesirable crop- i.e., cropping off most of the building’s height.

Distortion: +15

Vertical: -10

Horizontal: -8

Rotate: -.1

I’ve provided the slider settings to give you some idea of the magnitude of corrections needed. Of course, this process is even more effortless if you shoot with a lens already supported by Adobe’s profiles.

At any rate, it’s no big endeavor to correct architectural keystoning in Lightroom 3; in fact, it’s a rather speedy, enjoyable process! And, if you’re an architecture photographer who cannot justify dropping 2K on a tilt-shift lens(someday?), then Lightroom’s Lens Corrections provide a really sweet ticket to vertical-convergence-free photos!

5 Responses to Power of Post: Lens Corrections & Converging Verticals

Very interesting! I knew that this happened, but I didn't know the name for it.

I just found out yesterday that lensbaby has a tilt-transformer, which I was very excited about until it was discovered that it would only work with a Nikon mount lens on cameras that a lot of people don't have.